Provided is a synthetic peptide sp4 having an amino acid sequence as shown in SEQ ID No. 1. Said synthetic peptide, as the sole active ingredient in an anti-tumor pharmacodynamic test, has an inhibitory effect on both the tumor volume and tumor weight of human osteosarcoma MG-63 in nude mice. There is no difference between the relative tumor growth rate T/C (%) of the synthetic peptide sp4 and that of the positive control group of paclitaxel. The maximum tolerated dose for intravenous administration is 700 mg/kgBW. While having efficacy in vivo, the synthetic peptide sp4 has an inhibitory effect on tumor telomerase, has a blocking effect on G1 phase of the tumor cell cycle, and inhibits the high expression of tumor PD-L1 and CD47.